Add changelog
Add changelog

Copied from forum post here: https://social.msdn.microsoft.com/Forums/azure/en-US/39232c5e-547a-4688-ab42-c2a30dc51c01/changelog-for-mobile-apps-net-server-sdk-app-service?forum=azuremobile
aziel/azure-mobile-apps-net-server,brettsam/azure-mobile-apps-net-server,dhei/azure-mobile-apps-net-server,Azure/azure-mobile-apps-net-server,phvannor/azure-mobile-apps-net-server,brettsam/azure-mobile-apps-net-server,aziel/azure-mobile-apps-net-server,phvannor/azure-mobile-apps-net-server,dhei/azure-mobile-apps-net-server,brettsam/azure-mobile-apps-net-server,aziel/azure-mobile-apps-net-server,Azure/azure-mobile-apps-net-server